Fix test crashes related to AccountManagerHelper.

chrome/android/javatests/src/org/chromium/chrome/browser/test/ClearAppDataTestRule.java

 // Copyright 2017 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 package org.chromium.chrome.browser.test;
 
-import android.content.Context;
+import android.support.test.InstrumentationRegistry;
 
 import org.junit.rules.TestRule;
 import org.junit.runner.Description;
 import org.junit.runners.model.Statement;
 
 import org.chromium.chrome.test.util.ApplicationData;
 
 /**
  * JUnit test rule that just clears app data before each test. Having this as a rule allows us
  * to ensure the order it's executed in with something like RuleChain, allowing us to execute it
  * prior to launching the browser process.
  */
 public class ClearAppDataTestRule implements TestRule {
-    Context mContext;
-
-    public ClearAppDataTestRule(Context context) {
-        mContext = context;
-    }
-
     @Override
     public Statement apply(final Statement base, Description description) {
         return new Statement() {
             @Override
             public void evaluate() throws Throwable {
-                ApplicationData.clearAppData(mContext);
+                ApplicationData.clearAppData(InstrumentationRegistry.getContext());
             }
         };
     }
 }